1. Field of the Invention
The present invention relates to an inner-rotor type spindle motor which rotates and drives a magnetic disk such as a hard disk and a recording disk driving device including the spindle motor.
2. Background Art
FIG. 8 illustrates an inner-rotor type spindle motor including a conventional magnetic shield sheet. FIG. 8 is an axial cross-sectional view, wherein the vertical direction in the figure represents the axial direction. FIG. 9 is a main part top view of the spindle motor of FIG. 8 viewed from above.
The spindle motor includes a stationary assembly 1, a bearing 2, and a rotor assembly 3 which is rotatably supported by the bearing 2.
The stationary assembly 1 includes a stator 4 and an annular-shaped shield sheet 5. The shield sheet 5 is placed above the stator 4 to prevent magnetic fluxes generated from the stator 4 generally during driving from being largely leaked to the region above the shield sheet 5.
In recent years, there has been a need for size reduction, thickness reduction and price reduction of information devices such as hard-disk driving devices. Therefore, there has been also a need for size reduction, thickness reduction and price reduction of spindle motors installed in information devices.
However, in the conventional exemplary configuration of FIG. 8 and FIG. 9, if an attempt is made to reduce the thickness of the stator 4 in the axial direction for thickness reduction, a hook 4a of the stator 4 provided just below the shield sheet 5 will make impossible to place the shield sheet 5 below the hook 4a. This increases the difficulty of reducing the thickness of the stator 4.
Furthermore, since the shield sheet 5 is formed to cover the entire stator 4 from thereabove and also to cover a stator fitting portion 6a of the housing 6, a high material cost is required for the shield sheet 5. This increases the difficulty of fabricating an inexpensive shield sheet 5.